bytes to hex string

[random898989]

Ok this is embarrassing but what's Nim's equivalent of printf? In particular 
stringifying a bunch of bytes as a hex string? I see a format proc in strutils 
but it seems to only accept string varargs. I was trying to put together a 
crude guid generation function I have in Golang (see below) but I'm stumped.
    
    
    func guid() string{
        f, _ := os.Open("/dev/urandom", os.O_RDONLY, 0)
        b := make([]byte, 16)
        f.Read(b)
        f.Close()
        uuid := fmt.Sprintf("%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], 
b[10:])
        return uuid
    }
    
    
    
    proc guid():string=
        let f = open("/dev/urandom")
        var b:array[16, byte]
        discard readBytes(f, b, 0, 16)
        close(f)
        format("%x-%x-%x-%x-%x", b[0..4], b[4..6], b[6..8], b[8..10], b[10..15])
    

I understand I can use printf directly from C but don't know what function 
signature to use!

Thanks for any help!